Catalyzes the conversion of 17-oxosteroids to 17beta-hydroxysteroids . Favors the reduction of androstenedione to testosterone . Testosterone is the key androgen driving male development and function . Uses NADPH while the two other EDH17B enzymes use NADH . Androgens such as epiandrosterone, dehydroepiandrosterone, androsterone and androstanedione are accepted as substrates and reduced at C-17 . Can reduce 11-ketoandrostenedione as well as 11beta-hydroxyandrostenedione at C-17 to the respective testosterone forms .